Method of gettering impurities in electrical devices such as incandescent lamps



May 2, 1967 J. MARTIN ETAL 3,317,264 METHOD OF GETTERING IMPURITIES INELECTRICAL DEVICES SUCH AS INCANDESCENT LAMPS Filed Sept. 6, 1965 FIG.4.

PRELIMINARY LIGHT-UP OF FINISHED LAMP AT LOW VOLTAGE TO GETTERIMPURITIES WITHOUT RECRYSTALLIZING FILAMENT.

: FLASH FINISHED LAMP AT HIGH VOLTAGE TO RECRYSTALLIZE AND SET FTLAMENTUnited States Patent METHOD OF GETTERING IMPURITIES IN ELECTRICALDEVICES SUCH AS INCAN- DESCENT LAMPS Jack Martin, Paramus, and Hugh C.Hiner, Bloomfield, NJ., assiguors to Westinghouse Electric Corporation,Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 6, 1963, Ser.No. 307,146

8 Claims. (Cl. 316-25) This invention relates to a method of processingelectrical devices and has particular reference to a method of cleaningup residual impurities in tubular lamps after they have been sealed'andare ready for flashing.

During the manufacture of incandescent lamps it is very important thatthe lamp be kept free from material which would contaminate it andimpair its performance or life. This is particularly true in the case ofso called T3 quartz lamps now being marketed and used in heating andlighting applications. Such lamps are well known and consist of atubular quartz envelope that contains a coiled tungsten filament whichinitially has a fibrous unrecrystallized structure and is centrallysupported within the envelope. Since these lamps are very compact, theyare especially sensitive to impurities that remain on the filament orresidual gaseous impurities such as air that have not been removedbefore the envelope is sealed.

Despite all precautions, it frequently happens that small amounts ofimpurities are trapped in the sealed lamp. When the lamp is subsequentlyflashed to recrystallize and set the filament the impurities react withthe hot filament and form vapors which condense on the cool ends of thelamp envelope when they form a black deposit which is not only unsightlybut reduces the lamp efiiciency.

With the foregoing in mind, it is the general object of the presentinvention to provide a simple and economical method for cleaning upresidual impurities in a finished electrical device such as an electriclamp that contains an incandescible element.

Another and more specific object is the provision of a method forgettering impurities in completed electric incandescent lamps that canbe easily incorporated into high-speed manufacturing equipment and thatwill prevent blackening of the cooler portions of the lamp during thefilament-flashing operation.

The foregoing and other objects are achieved in accordance with thepresent invention by placing a suitable gettering material inheat-receptive proximity to the filament and then prelighting the lampat a predetermined voltage that is sutficient to heat the getter withoutrecrystallizing the filament or causing it to sag. The

impurities are thus liberated by the filament at a slower rate thanheretofore and the heated gettering material is able to absorb theimpurities before they condense on the envelope ends. The lamp remainslighted at this loW voltage for a short time, such as 20 seconds or so,and is then lighted at the usual high voltage to flash and recrystallizethe filament.

A better understanding of the invention will be obtained by referring tothe accompanying drawing, wherein:

FIGURE 1 is an elevational view of a tubular T3 heat lamp which isrepresentative of the type of device which can be processed by themethod of the present invention;

FIG. 2 is an enlarged cross-sectional view of the lamp along thereference line II-II of FIG. 1;

FIG. 3 is a fragmentary sectional view through the axis of the lampalong the reference line III-III of FIG. 2; and,

FIG. 4 is a block diagram illustrating the basic steps of the processaccording to a preferred embodiment of the present invention.

While the invention can be used with advantage in the manufacture ofvarious types of electrical devices having incandescible elements, it isespecially adapted for use in conjunction with tubular lamps designedfor heating or general lighting applications and it has, accordingly,been so illustrated and will be so described.

With particular reference to the drawing, in FIG. 1 there is illustrateda tubular T3 heat lamp 10 comprising a quartz envelope 12 that has adiameter of approximately and is closed at each end by a press seal 17and contains a linear filament 14 of coiled tungsten wire. The filamentis centrally disposed within the envelope and is held in this positionby means of attached lead-in con ductors 16 that are embedded in thepress seals and by a plurality of auxiliary support discs 18 that areattached to the filament at various points along its length. The lampcontains the usual inert gas filling such as argon at about 680 mm.pressure.

As shown more particularly in FIGS. 2 and 3 the support discs 18 are ofgenerally square configuration and are provided with a slot 22 thatextends inwardly from one of its sides to a centrally located aperture24. The discs are slightly smaller than the inner diameter of theenvelope 12 and are fabricated from a metal such as tantalum thatgetters gaseous impurities but does not react with or absorb the inertgas fill. The discs can be attached to the filament by inserting thembetween adjacent turns and spacing the latter so that they compressively clamp the discs in place as disclosed in US. Patent No.2,980,820, issued Apr. 18, 1961, to W. L. Brundige et al. a

The desired clean up of impurities that may inadvertently be trappedwithin the lamp after it has been sealed is accomplished in accordancewith the present invention by first lighting the lamp at a predeterminedvoltage below its rated voltage to vaporize and getter the impurities,and then flashing the lamp at a much higher voltage in the usual mannerto recrystallize and set the filament as outlined in the block diagramshown in FIG. 4.

In order to prevent the elongated filament 14 from developing apermanent sag when energized at either the low or high voltage, the lamp19 is preferably positioned in a magnetic field and a filtered D.-C.voltage of sufiicient magnitude is used to levitate the filament andmaintain it substantially straight while it is in a heated condition. Ofcourse, the magnitude and orientation of the magnetic field and thedirection and magnitude of the filament current must be properlycorrelated in order to achieve such levitation. The correct procedureand a preferred apparatus for achieving levitation of the energizedfilament is disclosed in copending application, Ser. No. 99,331, ofGordon B. Childs, entitled Apparatus for Flashing Lamp Filaments, filedFeb. 14, 1961, and assigned to the same assignee as the presentinvention, which application has now matured into US. Patent No.3,140,906.

rious sizes without recrystallizing the filament or causing it to sag inaccordance with this invention as given below J in Table I. Thecorresponding high-voltage flashing schedule is also listed for eachlamp type.

Lamps flashed in accordance with the high-voltage flashing schedulegiven in Table I heat the filament to The voltage and amperage listed inTable I above for the preliminary light-up are so correlated withrespect to the size and resistance of the filament that the latterreaches a temperature of about 1680 C. This temperature is preferredsince it enables the tantalum supports to reach a sufficiently hightemperature to become activated and quickly getter the gaseousimpurities liberated by and vaporized from the filament. Experience hasshown that if the lamps are simply flashed at the high voltages listedin the foregoing table without this preliminary low voltage light-up,the impurities are flashed off of the filament and onto the cool ends ofthe envelope with resultant blackening before the tantalum supportsreach a high enough temperature to absorb the impurities. While theexact nature of the impurities are unknown, it is believed that smallamounts of air may be trapped within the sealed lamps which, uponheating of the filament at the beginning of the highvoltage flashingoperation, react with the tungsten to form a thin oxide coating on thefilament. This oxide is then flashed off the filament and condenses onthe cool ends of the lamp envelope to form the undesirable blackeningeffect.

As will be apparent, the temperature to which the filament 14 is heatedduring the preliminary likht-up can be varied within rather wide limitsdepending upon the length of time the lamp is burned at this voltage.Since tungsten recrystallizes at a temperature of about 2100 C., it willbe seen that the preliminary light-up voltage and filament temperaturecan vary considerably from the aforementioned preferred values,providing the time of light-up is properly adjusted. Thus, the filamentternperatnre during the degasing and gettering operation can vary fromabout 1500 C. to 1850 C. and the time of light-up can vary from about to60 seconds without fully recrystallizing the filament or causing anobjectionable amount of sag. The preferred temperature range is,however, from 1600" C. to 1700 C. and the time of light-up is from about20 to 30 seconds.

As is well known, the ability of tantalum and other such metals togetter gaseous impurities increases with temperature. It is necessary,therefore, that the discs 18 reach a sufiiciently high temperature toprevent the liberated gases from reaching and blackening the cool endsof the envelope 12. At the aforementioned filament temperature rangesthe tantalum support dis-cs reach a temperature within the range ofapproximately 500 C. to 1400 C. with the hottest portions, of course,being those that are in direct contact with the filament. The heatedtantalum discs, accordingly, constitute very efficient getters andquickly clean up and absorb the gaseous impurities liberated by thefilament and other portions of the lamp structure before they canrecontaminate the finished lamp.

After the preliminary light-up and gettering operations have beencompleted the lamp is flashed at a much higher voltage in the regularmanner, as indicated by the block diagram in FIG. 4. However, thissecond step is optional as far as the cleaning-up operation is concernedsince substantially all of the impurities have been gettered during thepreliminary light-up. The second block in the diagram is, accordingly,shown in dotted lines to indicate that it can be omitted if desired.

a temperature in the order of 2700 C. so that recrystallization of thefilament occurs very rapidly. Thus, the configuration of the filament isset and will be substantially straight if a DC flashing voltage is usedand the filament is properly oriented within a magnetic field inaccordance with the teachings of the aforementioned copending patent ofGordon Childs.

It will be appreciated from the foregoing that the objects of theinvention have been achieved insofar as a very simple and inexpensivemethod of purging a completed lamp of deleterious impurities has beenprovided which method can be very conveniently incorporated intohigh-speed manufacturing apparatus, such as the flashing magneticapparatus disclosed and claimed in the foregoing copending patent ofGordon Childs.

While one embodiment has been disclosed in detail, it will beappreciated and understood that various modifications can be made in themethod without departing from the spirit and scope of the invention. Forexample, the filament can be flashed and recrystallized in a hydrogenatmosphere before the discs are mounted and the filament is sealedwithin the envelope. In this case, the low-voltage light-up would beperformed merely to clean up the impurities and recrystallization andfilament sag would not present any problem.

We claim as our invention:

1. In the manufacture of an electrical device having a sealed envelopethat contains an elongated incandescible filament which is designed tooperate at a predetermined rated voltage, the method of maintaining saidfilament in a predetermined position within said envelope and removingimpurities from said filament after it has been sealed Within saidenvelope and thereafter preventing such impurities from recontaminatingthe completed device, which method comprises:

attaching to said filament, prior to the assembly thereof with saidenvelope, a support member which (1) is adapted to engage a part of saidenvelope when the filament is disposed in assembled relationship withsaid envelope and (2) is composed of gettering material that is adaptedwhen heated to absorb gaseous impurities liberated by said filament;

placing said filament in assembled relationship with said envelope sothat the attached suppoit-gettering member interiorly engages theaforesaid part of said envelope;

sealing said filament in said envelope and completing the assembly ofsaid device;

heating said filament to a predetermined temperature below thetemperature which it attains when it is operated at its rated voltagebut which is sufficient to vaporize impurities associated with saidfilament without vaporizing the support-gettering member; and

maintaining the filament at said predetermined temperature for at leastseveral seconds so that the support-gettering member is heated by saidfilament and absorbs the vaporized impurities emanating from saidfilament.

2. In the manufacture of an electrical device having a sealed envelopethat contains an elongated filament of refractory metal wire which isdesigned to operate at a predetermined rated voltage and initially hasan unrecrystallized fibrous structure, the method of maintaining saidfilament in a predetermined position within said envelope and removingimpurities from said filament after it has been sealed within theenvelope and before it is flashed and set and thereafter preventing suchimpurities from recontaminating the completed device, which methodcomprises:

attaching to said filament, prior to the assembly thereof with saidfilament, a support member which (1) laterally protrudes beyond thefilament and is adapted to engage a part of said envelope when thefilament is disposed in assembled relationship with said envelope and(2) is composed of gettering material that is adapted when heated toabsorb gaseous impurities liberated by said filament;

placing said filament in assembled relationship with said envelope sothat the attached support-gettering member interiorly engages theaforesaid part of said envelope;

sealing said filament within said envelope and completing the assemblyof said device;

heating the unflashed filament to a predetermined temperature that isbelow its recrystallization temperature but sufficient to vaporizeimpurities carried by said filament and heat, but not vaporize, saidsupport-gettering member; and

maintaining the filament at said predetermined temperature for about 20'seconds to enable the heated support-gettering member to .absonb theliberated vaporized impurities without substantially recrystallizing thefialment.

3. In the manufacture of an electric device having a sealed envelopethat contains an incandescible filament of refractory metal wire thatinitially has an unrecrystallized fibrous structure and is subject tosag, the method of removing impurities from said filament after it hasbeen sealed into said envelope and before it is flashed andrecrystallized and preventing such impurities from subsequentlyrecontaminating the completed device, which method comprises:

mounting on said filament, prior to its assembly with said envelope, amember fabricated from a metal which when heated will getter gaseousimpurities liberated by said filament;

heating the unflashed filament to a temperature approximately 400 C.below its recrystallization temperature to activate said getteringmember solely by the heat imparted to it by said filament and vaporizeimpurities associated with said filament; and

maintaining the filament at said temperature for a period of about 20seconds so that said heated getter member absorbs substantially all ofthe liberated gaseous impurities before the filament becomesrecrystallized or develops an appreciable amount of sag.

4. The method set forth in claim 3 wherein said filament is heated bymeans of an electric current.

5. In the manufacture of an electric lamp having a tubular envelope thatcontains an elongated coiled filament of tungsten wire which initiallyhas a fibrous unrecrystallized structure and is susceptible to saggingbefore it is flashed and recrystallized, the method of removingimpurities from said filament after it is sealed within said envelopeand before it is flashed and set and preventing such impurities fromsubsequently contaminating the completed lamp, which method comprises:

attaching a tantalum member to said filament before it is sealed in saidenvelope, applying a voltage to the completed lamp suificient to heatthe filament to a temperature of from about 1500 C. to 1850 C. and thetantalum member to a temperature of about 500 C., and

continuing the application of said voltage for a period of time withinthe range of about 20 to seconds and sufiicient to enable the heatedtantalum member to absorb gaseous impurities liberated by the filamentwithout substantially recrystallizing the latter and causing it to sag.

6. The method set forth in claim 5 wherein; said tantalum membercomprises a disc that serves as a filament support, the applied voltageis such that the filament is heated to a temperature of from 1600 C. to1700 C. and the disc to a temperature of from 500 C. to 1400 C., and thefilament is maintained at said temperature for about 20 seconds.

7. In the manufacture of an electric lamp having a tubular envelope thatcontains an elongated coiled filament of tungsten wire which initiallyhas a fibrous unrecrystallized structure and is susceptible to saggingbefore it is flashed and recrystallized, the method of removingimpurities from said filament after it is sealed within said envelopeand before it is flashed and set and preventing such impurities fromsubsequently recontaminating the finished lamp, which method comprises:

attaching a tantalum support member to said filament before it is sealedinto said envelope,

applying a voltage to the finished lamp suflicient to heat the filamentto a temperature above about 1500 C. but below the recrystallizationtemperature of tungsten,

continuing the application of said voltage for a period of timesufiicient to heat the tantalum support member and enable it to gettergaseous impurities liberated by the filament without substantiallyrecrystallizing the latter, and then flashing the finished lamp at avoltage sufficient to recrystallize and set the filament.

8. The method set forth in claim 7 wherein; the filament is heated bymeans of direct current, said lamp is energized while the filament is ina magnetic field and disposed transverse to the lines of flux, and themagnitude and polarity of said current and magnetic field are socorrelated that the filament is levitated and prevented from saggingduring the gettering operation.

References Cited by the Examiner UNITED STATES PATENTS 2,489,261 11/1949Braunsdorfi 31625 X FRANK E. BAILEY, Primary Examiner.

3. IN THE MANUFACTURE OF AN ELECTRIC DEVICE HAVING A SEALED ENVELOPETHAT CONTAINS AN INCANDESIBLE FILAMENT OF REFRACTORY METAL WIRE THATINITIALLY HAS AN UNRECRYSTALLIZED FIBROUS STRUCTURE AND IS SUBJECT TOSAG, THE METHOD OF REMOVING IMPURITIES FROM SAID FILAMENT AFTER IT HASBEEN SEALED INTO SAID ENVELOPE AND BEFORE IT IS FLASHED ANDRECRYSTALLIZED AND PREVENTING SUCH IMPURITIES FROM SUBSEQUENTLYRECONTAMINATING THE COMPLETED DEVICE, WHICH METHOD COMPRISES: MOUNTINGON SAID FILAMENT, PRIOR TO ITS ASSEMBLY WITH SAID ENVELOPE, A MEMBERFABRICATED FROM A METAL WHICH WHEN HEATED WILL GETTER GASEOUS IMPURITIESLIBERATED BY SAID FILAMENT; HEATING THE UNFLASHED FILAMENT TO ATEMPERATURE APPROXIMATELY 400* C. BELOW ITS RECRYSTALLIZATIONTEMPERATURE TO ACTIVATE SAID GETTERING MEMBER SOLELY BY THE HEATIMPARTED TO IT BY SAID FILAMENT AND VAPORIZE IMPURITIES ASSOCIATED WITHSAID FILAMENT; AND MAINTAINING THE FILAMENT AT SAID TEMPERATURE FOR APERIOD OF ABOUT 20 SECONDS SO THAT SAID HEATED GETTER MEMBER ABSORBSSUBSTANTIALLY ALL OF THE LIBERATED GASEOUS IMPURITIES BEFORE THEFILAMENT BECOMES RECRYSTALLIZED OR DEVELOPS AN APPRECIABLE AMOUNT OFSAG.